Electrolytic reduction of sugars in acid solutions



plicate this work." See the published papersoi' Loeb, Z. Elektrochem, l6, 1 (-1910) of Findlay and Patented Oct. 27, 1942 nmc'monmc moo-nos or suoa'as is non) soLu'rroNs Ralph A. Hales, Tamaqna, Pa, assignor to Atlas Powder Com Wilmington, DeL, a corporation of Dela v No Application January Serial No. 219,705

14 Claims. (Cl. cos-m This invention relates to the electrolytic reduction of sugars to polyhydric alcohols and more particularly to such reduction while'maintaining the bulk of the sugar in an acid solution.

It has heretofore been proposed to electrolytically reduce glucose in an acid solution (see German patent to Gunn, No. 140, 818) but subdrogen thus fanned m the catholyte reduced the saccharide in the catholyte to a polyhydric alcohol.

- Now I have found that sugar may be successsequentinvestigations have not been able to du- Williams, Trans. Faraday $00., 17, 453 (1921- .1922) and of Hibbert and Read, J. A. C. 8., 46,

983' (1924) .My own attempts to duplicate the work of Gunn have likewise been wholly unsuccessful. u

The principal obiect of the present invention is to devise a highly successfulprocess for the electrolytic reduction of sugars while maintaining the bulk of the sugar throughout the reduction in an acid solution.

Another object of the present invention is to devise a process for the electrolytic reduction of sugars to polyhydric alcohols which yields a productofgreatly improved color-and color stability.

7 Other objects will more fully hereinafter appear.

fully reduced to a polyhydric alcohol while maintaining the main body of catholyte in acid condi= tion, provided the acid-catholyte contains an alkali metal sulfate. During',eiectrolysis, such a catholyte is made alkaline in the region immedi- V atelysurrounding the cathode so that reduction is made possible even though the main body of catholyte is acidic. There is a continuous formation or a thin film or layer oi alkaline catholyte around the cathode. The alkaline conditions .thus brought about at the cathode cause transformation of the saccharide to-a form in which itis reducible to a polyhydric alcohol by the action of the nascentfhyrogen liberated at the cathode.

In the process of the present invention, the catholyte is rendered acid prior to the g of reduction and is kept acid throughout the re- The process of reductionfand apparatus em ployed are similar to those disclosed in United States Letters Patent to Creighton, Number 1,990,582. In accordance with that patent, theelectrolytic reduction is carried out in a cell having a catholyte comprising an aqueous solution of one or more reducible saccharides and sodium sulfate or other suitable alkali metal compound. The catholyte is-in contact with-a cathode which servesto maintain the catholyte in an alkaline condition, and which is separated from the anoduction by the addition of amounts of acid from time to. time. The electrolytic action causes the/formation of alkali hydromde at the cathode from which it emanates into the catholyte, thereby tending to contin render the main body of the catholyte .4. e, and this must be prevented by neutralizing periodically in order to maintain the-main body or the catholyte on the acid side. a I

During reduction on the acid side in accordance with the process of this invention, the main body of the catholyte is at a pH of less than 7.0, and

lyte, comprising an aqueous solution of surfurifi acid, by a porous diaphragm. The porous dia- .ghragm perinits hydrogen ions to pass from the anode compartment-into the cathode compartment and permits the passage of sulphate ions .irom the cathode compartment to the anode com-- partmerit but is sumciently impermeable to prevent the diiIusion of the catholyte into the anode compartment. The anode in contact with the anohrte may consist of chemical lead 'or lead coated with lead dioxide. When electric current is passed through the cell, sulfate ions are dis charged at the anode, reacting with the water formingoxygen and sulfuric acid adjacent the anode. In the catholytic section of the call, so dium ions migrateto the cathode, are discharged accordingly the saccharide in the mainbody of the catholyie is. protected against the deleterious efiect. of a prolonged action of al ali hydroxide thereupon. As a result, thepolyhydric alcohol product of this invention is of better color, better thermalestability, and is lower in objectionable j impurities such as organic acids and alkali salts thereof. In addition to the production of a superior product, by reason of the elimination of the-degradative eflect of alkali upon the sugar, the reduction of saccharides to polyhydric'alcohol in accordance with the present invention is "married out at an economical speed. with high and unite with the water, forming nascenthy current efliciency and high yield. I

The acidity oi the main body of the catholyte may be varied from a pH of just wider-7.0 down I to a pH of 1.5 or even lower. In practice, due to the uneconomic reduotion'speeds obtained at a 'pH below 1.5, it will be found preferable to oper-' ate .at a pH notlowerthan 1.5, although where drogen and sodium hydroxide. 1 The nascent hy- 5 5 lower reduction speeds are'unobiectionable, a pH increased because of of below. 1.5 may be employed. Generally, it is recommended that the reduction be conducted with the main body of the catholyte at a pH of not lower than 2.3 because of the much greater reduction rate obtained.

The concentration of sugar'in will usually be in the neighborhood of 325 grams per liter although, obviously, smaller or larger amounts may be employed. Likewise, while the concentration of sodium sulfate or other alkali 'sulfatein the catholyte will usually be around 50 to 90, grams per liter, smaller or greater concentrations of this ingredient may be used. Thus,

' the catholyte may perhaps be explained by the statement that 'in the absence of an alkali'salt an alkali film cannot form on the surface of the cathode.

variations in sodium sulfate concentration of from 5 to 125 grams per litergive about the same rate of reduction under'otherwise identical conditions, and provided the pH is the same. How'- ever, for a givenpH the acidity in grams H2804 per liter increases as the alkali sulfate content is the buffer action of the alkali sulfate.

Any alkali sulfate may be used in the catholyte.

Sodium. sulfate is preferred on the ground of cheapness, but potassium sulfate gives somewhat higher rates. of reduction and may be used;

Ammonium sulfate gives a 'fair rate of reduction..

Lithium sulfate gives a lower rate of reduction than any of the other alkali sulfates mentioned and therefore while it may be-used, it is not pre-- 'ferred. v

The temperature of the cath'olyte during reduction is preferably maintained at around 69 F. although considerably higher temperatures may be employed. However, with all other clenditions the same, an increase in the temperature with the process of the present invention does not speed up the reduction, whereas when reducing with the main body of the ,catholyte alkaline, the efiect of an increase in temperature is to speed up the reduction. With the main body of the catholyte acidic, the failure of an increase in temperature to speed up the reduction may be attributed to a lowering of theviscosity ofthe catholyte at higher temperatures, causing a faster diffusion of the acid catholyte through the alkali film formed on the cathode.

The mechanism of reduction in the process of the present invention is not-clearly understood.

but it has been found that under the conditions employed thecathodes maintain a surroundingv layer of catholyte containing alkali hydroxide even though the main body of the catholyte is acid. Thus,an L-shaped tube with a capillary opening at the tip was slowly lowered into the catholyte at various times during the reduction,

' the tip being pointed towards and touching the cathode, and samples of the catholyte next to the sence of an alkali sulfate, I have found that it is 'impossible'to carry out reduction with the main .body of the catholyte in acid condition, and this.

ample 1.? below.

In carrying out the process of the presentinvention, the effect of the use of higher current densities is to permit the use of a catholyte of lowerpH. An increase in current density appears to cause an increase in the rate of formation of the alkali film on the cathode, which increased rate seems to counteract the tendency of catholytes ofhigh acidity to slow up the reduction. The effect of variations in current density upon the rate of reductionis, therefore, much more pronounced when employing the process of the present invention than when carry ng out a reduction with the main body of the catholyte on the alkaline side.

The .cathodes employed in carrying out the reduction-may be of amalgamated solid metal such as amalgamated zinc 'or lead, or of suitable unamalgamated metal such as zinc, or of carbon or graphite. I 1 While the invention is particularly applicable to the reduction of monosaccharides, one of its advantagesis that it may be applied to disaccharides such as sucrose, which may be inverted .by

the acid in the catholyte and substantially simul-' taneously the monosaccharlde inversion products may be reduced to the corresponding polyhydric alcohols. An example of such procedure is Ex- The invention is also applicable'to the direct reduction of reducible oligo-saccharides .such as reducible disaccharides, such as lactose, to the corresponding polyhydric alcohol. S An example of this is Example 18 below wherein lactose reduced directly to lactositol.

The process of the, present invention has a marked advantage over reductions wherein the main body of thecatholyte is alkaline in that the present process yields 'aproduct of improved properties. Thus, the thermal stability of the products of the present process is outstanding.

Sorbitol syrup made in accordance with the present invention increases in color only very slightly upon heating, say from 6 to 22 /2 hours at 90 C., and is in this respect greatly superior to sorbitol syrups produced with the main body of catholyte in-alkaline condition. .Th'e improved thermal stability is due to the very small proportions of colon-forming bodies .present in' the product.

' Formation of these color-forming bodies is precatholyte.

' cathode ere taken. These samples were all vented by the elimination of the, destructive action of alkaliupon thesugar and upon the products of reduction in the main body of the Below are a number of non-limiting. specific examples of reductions wherein the main body of the catholyte was acid. In each example the catholyte was processed in accordance with the process disclosed'in U. S. Patent 2,116,665 to recover the polyhydric alcohol therefrom.

. against prolonged attack by. alkali. In the"ab- Y Example 1- I Glucose was. electrolytically reduced to a sorbital syrup at amalgamated lead cathodes at a temperature of 68 F. The catholyte was anadueous solution of glucose, sodium sulfate and 'sulfuric'acid in the. proportions of 325 grams of magnesium-free glucose per liter, grams of magnesium-free sodium sulfate per liter and 0.1 gram of magnesium-free H2804 per liter. The anolyte was an aqueous solution. of 300- grams C. P. sulfuric acid per liter. The volum'eof catholyte used was 3.36 liters, and the cathode surface was 8.15 square decimeters. The current density at the cathode-was 1.10 amperes per square decimeter during the firstpart of reduction and after approximately 65% of the sugar had been reduced, which was'after 50 hours, it

.was reduced to 0.55. The main body of ,the catholyte was maintained at an acidity of approximately 0.1 gram per liter and pH of approximately 3.6 throughout the reduct on by the addition to the catholyte of the required amounts of sulfuric acid at frequent periodic intervals during the reduction. After 117 hours, when the glucose was- 87.8% reduced, the cell was shut down. The-yield of polyhydric alcohol was 97.8% of the theoreticaL The product was a sorbitol syrup having a pyridine number of 83.0.

Example 2 This reduction was carried out following identically the conditions of Example 1 except that the catholyte was maintained at an acidity of about 1.0 gram H2804 per liter andat a pH of approximately 2.2. The current density was re duced from 1.1 to 0.55 amps. per sq. dm. after 67 to reduce glucose under identically the same conditions as above but using no alkali sulfate in the catholyte and using an anolyteconsisting of an aqueous solution of only 250 grams H2804 per liter. A current density of 1.1 amps. per sq. dm.

' water-white sorbitol Example v5 Glucose was reduced under the same conditions as in Example 1 except that the temperature was 72 F. The acidity was maintained throughout at between 0.1 and 1.5 gms. H2804 per liter, the initial acidity being 1.5 gm. H2804 per liter. As in Example 1 the current density was reduced from 1.1 to 0.55 amps per sq. dm., whena roximately 65% of the sugar was reduced, whi was at 42. hours. In 205 hours the glucose was 98.5% reduced and the run was ended. The yield was 93.0% of the theoretical. The product was 'a syrup having a pyridine number of 65.0. I

Example 6 Glucose was reduced underthe same conditions as in Example 5, except that the current density was maintained throughout at 1.1, amps. per sq. dm. instead of being lowered to 0.55 when 65% bi the sugar had been reduced. The rate of reduction during the latter part of the run was increased by employing the higher current density duri'ng that portion of the run. The glucose was 99.0% reduced after 134 hours, at which time the run was ended. The yield was 96.1% of the theoretical and the product was a water-white sorbitol syrup having a pyridine number of 74.5.

was used throughout the run except in the latter part where this current density could not be maintained on account of the high voltage at low acidity. Sulfuric acid was added to the catholyte as required to maintain the acidity at a. pH of approximately 2.2. The current was passed for 72.3 hours when tests showed that no sugar had been reduced. Thereupo'n the run was ended.

No product was obtained.

1, except that the temperature was 72 F. and the acidity ofthe main body of the catholyte was maintained at between 0.1 and 0.5 gram H2SO4 per liter, being 0.4 gram per liter at thestart. Appropriate periodic additions of H2804 were made to keep the acidity within the above range. The sugar was approximately 65% reduced after 32 hours of operation, at which time the current density was reduced-from 1.1 to 0.55 amps. per sq. dm. After 116 hours 98.6% of the sugar had been reduced and the run was ended. The yield of polyhydric alcohol was 90.2% of the theoretical. The product was a sorbitol syrup having a pyridine number of 73.5.

Example '4 This was like Example 3 except thatthe tem perature was 76' F. and the acidity of the catholyte washetween 0.1 and 0.7-gram H1804 per liter.

The glucose was approximately 65% reduced after 42 hours,- at which time the current density was reduced from 1.1 to 0.55 amps. per sq. dm. After 142- hours, 99.0% of the glucose had been reduced Example 7 gm. H2804 per liter and a pH of arpund 2.7.

The catholyte solution originally contained 325 gms. magnesium-free glucose per-liter, and

gms. magnesium-free sodium sulfate. In 104 hours the sugar was 99.0% reduced. The yield of polyhydric alcohol was 90.8%. of the theoretical.

The product was a water-white sorbitol syrup tremely low0.01% (reported as sodium sulfate).

, Example 8' diiced'in l0l. hours. The yield was 92% of the Y theoretical. e product was a water-white sorbitol syrup having a pyridine number of 62 and an organic acid sodium salt content of 0.04% (reported as sodium sulfate).

Example 9 Glucose was reduced under the same conditions as in Example 7' except that the temperature was maintained at F. The glucose was 98.4% reduced in 99 hours'. The yield was 86.7% of the theoretical. The product was a very light lemon 65- colored sorbitol syrup having a pyridine number of 42 and an organic acid sodiumsalt content of 0.10% (reported as sodium sulfate).

Example 10 Glucose was reduced exactly as in Example 7 except that the acidity was greatenbeing maintained at between 1.5 and 2.5, gms. H2804 per liter at a pH of around and that the catholyte contained 69 gms. of Na: 04 per liter. The sugar was 94.4% reduced after 31 hours. The

g yield was 87.3% of the theoretical. .The product was a water-white sorbitol syrup having a pyridine number of 70.0 and no measurable organic acid sodiumsalt content.

' Example 11 Glucose was reduced under the same conditions as in'Example except that 75 grams of magnesium-free ammonium sulfate per liter wereused as the alkali sulfate. The sugar was 94.9% reduced in 339 hours and the yield of polyhydric alcohol was 88.7% of thetheoretical. The product was a sorbitol syrup havinga pyridine number of 77.5.

- Example 12 Glucose was reduced under the same conditions as in'Example 10 except that 69 gms. of magnesium-free potassium sulfate per liter were used as the alkali sulfate and the acidity of the main body of the catholyte was maintained at between 1 and 2 gms. H2804 per liter and the pH at approximately 2.3. After 121 hours the glucose was 99.1% reduced. Theyield of polyhydric a1 per liter. After 114 hours only 25.8% of the glu-' cose had beenreduced and the run was thereupon ended. The yield of polyhydric alcohol was 92.1% of the theoretical. The product was a sorbitol syrup.

Example 14 Glucose was electrolytically reduced at amalgamated zinc cathodes in a catholyte containing 325 gms. of magnesium-free glucose per liter, 75 gms. of magnesium-free sodium sulfate per liter, the main body of the catholyte being maintained at an acidity of from 2.5 to 3.5 gms. H2804 per liter and at'a pH of approximately 2.1."The cur-' rent density was maintained at 1.0 amps. per sq. dm. of cathode area. The ratio of cathode area in sq. dm. the catholyte volume in liters was been reduced and the run was thereupon dis- 2.0. After 137 hours 48.9% of the sugar'had continued. The yield of polyhydric alcohol (sor bitol)v was 87.0% of theoretical.

Example 15 Glucose was reduced exactly as in Example 14 except that 75 grams of K2804 per liter were maintained at 74 F. The ratio of cathodearea. to catholyte voluine was 2.0 sq. per liter. The pH was maintained throughout the 'reduc- 7 tion at approximately 1.9 andth acidity at 3.5

to 4.5 gms. HzSOi per liter of catholyte. After 42 hours, 99% of the glucose was reduced. The

used as the alkali'sulfate. "After 193 hours 87.0%

of the glucose-had been reduced. Subsequent reduction was very slow for after 239 hours only 88.0% of the glucose had been reduced. The

run was .then ended. The yield of polyhydric alcohol was 85.0% of the theoretical. The productv was a water-white sorbitol syrup having'a pyridine number of 75.0 and containing organic acid sodium salt content of 0.07% (reported asgso dium sulfate).

, Example 16 Glucose was. reduced at amalgamated zinc cathode, thecatholyte initially containing 325' gins. glucose per liter and 75 gms. NazSO per.

liter.

sq. dm. of cathode area. The temperature was.

The current density was 4.0 amps. per

current efiiciency. was 27.2%. a The product was a waterwhite,sorbitol syrup having a pyridine number of 66.5, and. an organic acid sodium salt content of 0.02% calculated as sodium sulfate.

The yield was 95.4% of the theoretical.

Example 17 This example shows substantially simultaneous inversion of a non-reducible disaccharide and re-' duction of the inversion products, yielding two polyhydric alcohols.

An aqueous solution of sucrose containing 325 gms. sucrose per liter was acidified with H2804 to a pH of 2.3. It was then placed in the oathode compartment of an electrolytic reduction cell having amalgamated zinc cathodes, and reduction was begun. The current density was 1.0 amp. per sq. dm. and the temperature was maintained at 81 F. The 'ratio of cathode area to catholyte volume was 1.21 sq. dm. per liter. Agelatively large volume of solution (1. e. a low sq. dm./L ratio) was used so that the rate of in- I version of the sucrose would be appreciably higher than the rate of reduction of the invert sugar so produced, and so that reduction might not be delayed by. reason of an insumcient'concentration of invert sugar in the catholyte, sucrose beingnot directly reducible because of its molecular configuration. The concentration of H2804 was maintained at between 1-2 gms. H2804 per liter. The initial concentration of sodium sulfate in the catholyte was gms. per liter. After 425 hours 90% of the sucrose had been inverted and reduced. The current eiliciency was 16.1%. The

yield was 90.3% of the theoretical. The product consisted of man'nitol in an amount equal to 18.0% of the total polyhydric alcohol yield and a water-white sorbitol syrup having apyrldine number of 52.0 and an organic acid sodium salt;

content of 0.03% calculated as sodium sulfate.

Example 18 I This example shows reduction of a reducible disaccharide directly to the corresponding polyhydric alcohol, no appreciable inversion of the disaccharide' taking place.

Lactose in the form of'an aqueous solution containing 325 grams of lactose monohydrate was reduced in an electrolytic cell at amalgamated zinc cathodes. The current density was 1.0 amp.

'per sq. dm. The temperature was maintained at F. The ratio of cathode area to catholyte volume was 1.21 sq. dm. per liter. The

initial'pH was 2.3. The aciditywa's'maintained v at 1.5-2.5 gms. H2804 per liter. 'I'he initial soliter.

dium sulfate concentration was 75 gms. per of the sugar had been reduced in 660 hours. The current efliciency was 4.9%. The product was a water-white syrup consisting chiefly .of lactositol. No polyhydric alcohol of limited solubility in watensuch as mannitol or dulcitol, was formed in appreciable amountaand the pyridine number of the syrup was 0.0. From the foregoing descriptionit will be seen that .I have-devised a successful process for'the electrolytic reduction of reducible saccharides to polyhydric alcohols while maintaining the main body of thecatholyte on the acid side. which catholyte within results in numerous advantages. among which is the greatly reduced opportunity for alkali degradation of the sugar with the consequent production of objectionable color, of high organic acid content, of poor heat-stability of the product, etc.

In this specification and in the claims appended hereto, by the expression main body of the catholyte" I meanthe entire catholyte with the exception of a film of-catholyte surround the cathode, which fllm is maintained in an alkaline condition at the cathode by electrolysis with a catholyte containing an alkali metal sulfate, as=

herein explained. ,By reducible saccharides" I mean the mono-saccharides, and the oligosac charides which will reduce Fehlings solution, these being the saccharides which are directly reducible to polyhydric alcohols.

Having described my invention, what i claim '1. The process for producing a sorbital-containing product which comprises electrolyticallyalkali metal sulfate as.the catholyte in contact with the cathode in the catholyte compartment of an electrolytic diaphragm cell, and maintaining the catholyte at a pH of substantially less:

than 7.0 and not lower than about 2.3 throughout the reduction.

3. The process for producing polyhydric alco hol which comprises electrolytically reducinga reducible sugar in an aqueous solution compris sulfate and sulfuric acid as the catholyte in contact with the cathode inth catholyte commit-- ment of an electrolytic diap agm cell,said acid being present in amount sufilcient to give the catholyte a pH of substantially less than 7.0 and not lower than about 1.5, and maintaining the catholyte at a pH substantially below 7.0 and not less than about 1.5.throughout the reduction.

7. The process for producing polyhydric alcohol which comprises electrolytically reducing a reduciblesugar in -an aqueous solution comprising an alkali. metal sulfate and sulphuric acid the catholyte compartment of an electrolytic as the catholyte in contact with the cathode in diaphragm cell, and maintaining the pH of'the catholyte substantially below 7.0 and not less than about 1.5 throughout the reduction.

-8. The process for producing polyhydricalcohol which comprises electrolytically reducing a re-- ducible sugar in an aqueous solution with sulfuric acid as the catholyte in contact with the cathode in the catholyte compartment of an electrolytic diaphragm cell; said catholyte further comprise in contact with the ca ing a substantial amount of acid and an alkali metal sulfate as the catholyte in contact with the cathode in the catholyte compartment of an electrolytic diaphragm cell, said acid being present in amount. to give the catholyte a pH substantially less than 7.0 and not lower than about 1.5, and continuously maintaining the pH of the duction. I

4. The process for producing a hexitol-conta n product which comprises electrolytically reducing a monosaccharide in an aqueous solution comprising substantial amounts of an alkali metal sulfate and of sulphuric acid as the said values throughout the recatholyte in contact with the cathode in the catholyte compartment of an electrolytic diaphragm cell, and maintaining the catholyte at a pH substantially less than 7.0 and not lower than about 1.5 throughout the reductiom 5. The process for producing polyhydric alcohol-whichcoinprises electrolytically reducing a reducible sugar in an aqueous solution comprising substantial amounts of an alkali metal sulfate andsulfuric acid as the catholyte in contact with-the cathode in the catholyte compartment of an electrolytic diaphragm cell, and maintaining the catholyte at a pH substantially less than 7.0 and not less than about.2.3 throughout the reduction.

6. The process for producing a sorbitol-con taining product which comprises electrolytically reducing glucose in anaqueous solution comprising from 5 to 125 grams sodium sulfate per liter,

and maintaining the pH of the catholyte substantially less than 7.0and not less than about 1.5 during the reduction.

9. The process-for producing polyhydric alcohol which comprises substantially simultaneously inverting a disaccharide in an aqueous solution with a strong acid and electrolytically re-' ducing the inversion products as the catholyte ode in the catholyte compartment of an electrolytic diaphragm cell, said catholyte comprising a substantial amount of an alkali metal sulfate, and maintaining said catholyte at a pH substantially less than 7.0 and not less than about 1.5 throughout the reduction.

10. The process for producing. polyhydric alcohol which comprlsessubstantially simultaneously inverting sucrose in an aqueous solution with a substantial amount of a strong acid and electrolytically reducing the inversion products .as the catholyte in contact with the cathode in the catholyte compartment ofan electrolytic dia-' phragm cell, said cathglyte comprising a sub-.

stantial amount of analkali metal sulfate, and maintaining said catholyte at a pH substantially below 7.0 and not less than about 15 throughout the reduction. 11. The process for producing polyhydric alco hol which comprises substantially simultaneously inverting sucrose in a substantially acid aqueous sulfuric acid solution and electrolytically reducing the inversion-products-as the catholyte" in contact with the cathode in the catholyte compartment .of an electrolytic diaphragm cell,

- said catholyte comprising a substantial amount oohol which comprises electrolytically reducing a reducibledisaccharide in an aqueous solution comprising substantial amounts of strong acid and an alkali metal sulfate as the catholyte in contact with the cathode in the catholyte com-' partment of an electrolytic diaphragm 'cell, and

maintaining said catholyte at a pH substantially less than 7.0 and not less than about 1.5 throughout the reduction.

13. The process for producing lactositol which comprises electrolytically reducing lactose in an ing substantial amounts of an alkali metal aqueous solution comprising substantial amounts of strong" acid and an alkali metal sulfate as the catholyte in contact with the cathode in the catholyte compartment of an electrolytic diaaqueous solutioh comprising substantial amounts of sulfuric acid and an alkali metal sulfate as,

the catholyte in contact-with the cathode in the catholyte compartment of an electrolytic diaphragm cell, and maintaining saidcatholyte at a pH substantially below 7.0 and not less than about 1.5 throughout thereductlon.

RALPH A. HALES. 

